=No. 49.= Two sheets of aluminum-leaf for the leaf electroscope (Fig. 57) and other experiments. =No. 50.= One bent wire (H P, Fig. 57) used in connection with the leaf electroscope. =No. 51.= A dry cell, ordinary size about 7 in. high and 2-1/2 in. in diameter. =No. 52.= Enough mercury to amalgamate battery zincs. A wooden pill box containing about half a thimbleful will do. =No. 53.= A coil containing 25 feet of No. 24 insulated copper wire for connections. =No. 54.= One dozen spring connectors (Fig. 61) for making connections. These are made of brass, nickel plated, and do not affect the compass-needle. =No. 55.= A telegraph key (Fig. 68) without switch. The metal straps are made of aluminum; they are 1/2 in. wide, and are fastened to a neat wooden base. =No. 56.= Three metal plates, each about 2 in. by 3/4 in., on which spring connectors (No. 54) are to be pushed in order to join two wires. =No. 57.= A current reverser (Fig. 69). The straps are made of aluminum and are fastened to a neat wooden base. =No. 58.= A galvanoscope (Fig. 72) including a degree-card (No. 99). The cardboard coil-support, C S, is 5 × 6-1/4 in., and the hole in it is 3-3/8 in. in diameter. The coil is 4-1/4 in. in diameter, made of No. 24 insulated copper wire. =No. 59.= An astatic galvanoscope (Fig. 77). The whole may be taken apart and mailed in the containing box, B, which is 4-3/8 × 3-1/8 × 1 in. The coil is made of No. 31 wire, and has a resistance of about 5 ohms. Spring connectors are used to join a wire to the apparatus by pushing the connectors into the tubular binding-posts, L and R. =No. 60-63.= Four strips of sheet zinc, 4 in. by 1/2 in., not amalgamated. =No. 64.= A carbon rod, 4 in. long (Fig. 81). =No. 65, 66.= Two glass tumblers (Fig. 81). =No. 67, 68.= Two strips of sheet copper, 4 in. by 1/2 in. (Fig. 85). =No. 69.= One galvanized iron nail. =No. 70, 71.= Two wooden cross-pieces (Fig. 85). =No. 72.= One dozen brass screws, 5/8 in. long, size No. 5, with round heads. =No. 73.= A porous cup (P C, Fig. 87) that will stand inside of the tumblers (No. 65). =No. 74.= A zinc rod, about 3/8 in. in diameter, like those used in Leclanché cells. =No. 75.= A sheet copper plate for the two-fluid cell (C, Fig. 87). This is 2 in. wide; it nearly surrounds the porous cup, and is supported upon the edge of the tumbler by a narrow strip, A, with which connections are made by spring connectors (No. 54). =No. 76.= One strip of sheet iron, 4 in. by 1/2 in. =No. 77, 78.= Two strips of sheet lead, 4 in. by 1/2 in. =No. 79.= A resistance coil (Fig. 94). The coil is made of No. 24 insulated copper wire; it has a resistance of 2 ohms (nearly) and is fastened to a cardboard base. It is so arranged that either one or two ohms can be used at will.